Beginners introduction to ASP.NET

1. Naveen Kumar Veligeti
Beginners Introduction to ASP.NET
Introduction
I have seen many tutorials on ASP.NET but most of them starts with coding and writing your first
ASP.NET Program. But here I has written this tutorial for explaining why there is a need for ASP.NET
when classy ASP is working fine and what are the underlying technology behind ASP.NET, What
programming model ASP.NET Provides to programmers. Now let us get started.
ASP.NET is the new offering for Web developers from the Microsoft .It is not simply the nextgeneration of ASP; in fact, it is a completely re-engineered and enhanced technology that offers
much, much more than traditional ASP and can increase productivity significantly.
Because it has evolved from ASP, ASP.NET looks very similar to its predecessor—but only at first
sight. Some items look very familiar, and they remind us of ASP. But concepts like Web Forms, Web
Services, or Server Controls gives ASP.NET the power to build real Web applications.
Looking Back : Active Server Pages (ASP)
Microsoft Active Server Pages (ASP) is a server-side scripting technology. ASP is a technology that
Microsoft created to ease the development of interactive Web applications. With ASP you can use
client-side scripts as well as server-side scripts. Maybe you want to validate user input or access a
database. ASP provides solutions for transaction processing and managing session state. Asp is one
of the most successful language used in web development.
Problems with Traditional ASP
There are many problems with ASP if you think of needs for Today's powerful Web applications.
1. Interpreted and Loosely-Typed Code
ASP scripting code is usually written in languages such as JScript or VBScript. The script-execution
engine that Active Server Pages relies on interprets code line by line, every time the page is called. In
addition, although variables are supported, they are all loosely typed as variants and bound to
particular types only when the code is run. Both these factors impede performance, and late binding
of types makes it harder to catch errors when you are writing code.
2. Mixes layout (HTML) and logic (scripting code)
ASP files frequently combine script code with HTML. This results in ASP scripts that are lengthy,
difficult to read, and switch frequently between code and HTML. The interspersion of HTML with ASP
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code is particularly problematic for larger web applications, where content must be kept separate
from business logic.
3. Limited Development and Debugging Tools
Microsoft Visual InterDev, Macromedia Visual UltraDev, and other tools have attempted to increase
the productivity of ASP programmers by providing graphical development environments. However,
these tools never achieved the ease of use or the level of acceptance achieved by Microsoft Windows
application development tools, such as Visual Basic or Microsoft Access. ASP developers still rely
heavily or exclusively on Notepad.
Debugging is an unavoidable part of any software development process, and the debugging tools
for ASP have been minimal. Most ASP programmers
resort to embedding temporary Response. Write statements in their code to trace the progress of its
execution.
4. No real state management
Session state is only maintained if the client browser supports cookies. Session state information can
only be held by using the ASP Session object. And you have to implement additional code if you, for
example, want to identify a user.
5. Update files only when server is down
If your Web application makes use of components, copying new files to your application should only
be done when the Web server is stopped. Otherwise it is like pulling the rug from under your
application's feet, because the components may be in use (and locked) and must be registered.
6. Obscure Configuration Settings
The configuration information for an ASP web application (such as session state and server timeouts)
is stored in the IIS metabase. Because the metabase is stored in a proprietary format, it can only be
modified on the server machine with utilities such as the Internet Service Manager. With limited
support for programmatically manipulating or extracting these settings, it is often an arduous task to
port an ASP application from one server to another.
Introducing ASP.NET
ASP.NET was developed in direct response to the problems that developers had with classic ASP.
Since ASP is in such wide use, however, Microsoft ensured that ASP scripts execute without
modification on a machine with the .NET Framework (the ASP engine, ASP.DLL, is not modified when
installing the .NET Framework). Thus, IIS can house both ASP and ASP.NET scripts on the same
machine.
Advantages of ASP.NET
1. Separation of Code from HTML
To make a clean sweep, with ASP.NET you have the ability to completely separate layout and
business logic. This makes it much easier for teams of programmers and designers to collaborate
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efficiently. This makes it much easier for teams of programmers and designers to collaborate
efficiently.
2. Support for compiled languages
developer can use VB.NET and access features such as strong typing and object-oriented
programming. Using compiled languages also means that ASP.NET pages do not suffer the
performance penalties associated with interpreted code. ASP.NET pages are precompiled to bytecode and Just In Time (JIT) compiled when first requested. Subsequent requests are directed to the
fully compiled code, which is cached until the source changes.
3. Use services provided by the .NET Framework
The .NET Framework provides class libraries that can be used by your application. Some of the key
classes help you with input/output, access to operating system services, data access, or even
debugging. We will go into more detail on some of them in this module.
4. Graphical Development Environment
Visual Studio .NET provides a very rich development environment for Web
developers. You can drag and drop controls and set properties the way you do in Visual Basic 6. And
you have full IntelliSense support, not only for your code, but also for HTML and XML.
5. State management
To refer to the problems mentioned before, ASP.NET provides solutions for session and application
state management. State information can, for example, be kept in memory or stored in a database. It
can be shared across Web farms, and state information can be recovered, even if the server fails or
the connection breaks down.
6. Update files while the server is running!
Components of your application can be updated while the server is online and clients are connected.
The Framework will use the new files as soon as they are copied to the application. Removed or old
files that are still in use are kept in memory until the clients have finished.
7. XML-Based Configuration Files
Configuration settings in ASP.NET are stored in XML files that you can easily read and edit. You can
also easily copy these to another server, along with the other files that comprise your application.
ASP.NET Overview
Here are some point that gives the quick overview of ASP.NET.
ASP.NET provides services to allow the creation, deployment, and execution of Web Applications and
Web Services
Like ASP, ASP.NET is a server-side technology
Web Applications are built using Web Forms. ASP.NET comes with built-in Web Forms controls,
which are responsible for generating the user interface. They mirror typical HTML widgets like text
boxes or buttons. If these controls do not fit your needs, you are free to create your own user
controls.
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Web Forms are designed to make building web-based applications as easy as building Visual Basic
applications
ASP.NET Architecture
ASP.NET is based on the fundamental architecture of .NET Framework. Visual studio provide a
uniform way to combine the various features of this Architecture.
Architecture is explained form bottom to top in the following discussion.
1. At the bottom of the Architecture is Common Language Runtime. NET Framework common
language runtime resides on top of the operating system services. The common language runtime
loads and executes code that targets the runtime. This code is therefore called managed code. The
runtime gives you, for example, the ability for cross-language integration.
2. .NET Framework provides a rich set of class libraries. These include base classes, like networking and
input/output classes, a data class library for data access, and classes for use by programming tools,
such as debugging services. All of them are brought together by the Services Framework, which sits
on top of the common language runtime.
3. ADO.NET is Microsoft’s ActiveX Data Object (ADO) model for the .NET Framework. ADO.NET is not
simply the migration of the popular ADO model to the managed environment but a completely new
paradigm for data access and manipulation.
ADO.NET is intended specifically for developing web applications. This is evident from its two major
design principles:
1. Disconnected Datasets—In ADO.NET, almost all data manipulation is done outside the context of an
open database connection.
2. Effortless Data Exchange with XML—Datasets can converse in the universal data format of the Web,
namely XML.
4. The 4th layer of the framework consists of the Windows application model and, in parallel, the Web
application model.
The Web application model-in the slide presented as ASP.NET-includes Web Forms and Web
Services.
ASP.NET comes with built-in Web Forms controls, which are responsible for generating the user
interface. They mirror typical HTML widgets like text boxes or buttons. If these controls do not fit
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your needs, you are free to create your own user controls.
Web Services brings you a model to bind different applications over the Internet. This model is based
on existing infrastructure and applications and is therefore standard-based, simple, and adaptable.
Web Services are software solutions delivered via Internet to any device. Today, that means Web
browsers on computers, for the most part, but the device-agnostic design of .NET will eliminate this
limitation.
5. One of the obvious themes of .NET is unification and interoperability between various programming
languages. In order to achieve this; certain rules must be laid and all the languages must follow these
rules. In other words we can not have languages running around creating their own extensions and
their own fancy new data types. CLS is the collection of the rules and constraints that every language
(that seeks to achieve .NET compatibility) must follow.
6. The CLR and the .NET Frameworks in general, however, are designed in such a way that code written
in one language can not only seamlessly be used by another language. Hence ASP.NET can be
programmed in any of the .NET compatible language whether it is VB.NET, C#, Managed C++ or
JScript.NET.
Quick Start :To ASP.NET
After this short excursion with some background information on the .NET Framework, we will now
focus on ASP.NET.
File name extensions
Web applications written with ASP.NET will consist of many files with different file name extensions.
The most common are listed here. Native ASP.NET files by default have the extension .aspx (which is,
of course, an extension to .asp) or .ascx. Web Services normally have the extension .asmx.
Your file names containing the business logic will depend on the language you use. So, for example,
a C# file would have the extension .aspx.cs. You already learned about the configuration file
Web.Config.
Another one worth mentioning is the ASP.NET application file Global.asax - in the ASP world formerly
known as Global.asa. But now there is also a code behind file Global.asax.vb, for example, if the file
contains Visual Basic.NET code. Global.asax is an optional file that resides in the root directory of
your application, and it contains global logic for your application.
All of these are text files
All of these files are text files, and therefore human readable and writeable.
The easiest way to start
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The easiest way to start with ASP.NET is to take a simple ASP page and change the file name
extension to .aspx.
Page Syntax
Here is quick introduction of syntax used in ASP.NET
Directives
You can use directives to specify optional settings used by the page compiler when processing
ASP.NET files. For each directive you can set different attributes. One example is the language
directive at the beginning of a page defining the default programming language.
Code Declaration Blocks
Code declaration blocks are lines of code enclosed in <script> tags. They contain the runat=server
attribute, which tells ASP.NET that these controls can be accessed on the server and on the client.
Optionally you can specify the language for the block. The code block itself consists of the definition
of member variables and methods.
Code Render Blocks
Render blocks contain inline code or inline expressions enclosed by the character sequences shown
here. The language used inside those blocks could be specified through a directive like the one
shown before.
HTML Control Syntax
You can declare several standard HTML elements as HTML server controls. Use the element as you
are familiar with in HTML and add the attribute runat=server. This causes the HTML element to be
treated as a server control. It is now programmatically accessible by using a unique ID. HTML server
controls must reside within a <form> section that also has the attribute runat=server.
Custom Control Syntax
There are two different kinds of custom controls. On the one hand there are the controls that ship
with .NET, and on the other hand you can create your own custom controls. Using custom server
controls is the best way to encapsulate common programmatic functionality.
Just specify elements as you did with HTML elements, but add a tag prefix, which is an alias for the
fully qualified namespace of the control. Again you must include the runat=server attribute. If you
want to get programmatic access to the control, just add an Id attribute.
You can include properties for each server control to characterize its behavior. For example, you can
set the maximum length of a TextBox. Those properties might have sub properties; you know this
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principle from HTML. Now you have the ability to specify, for example, the size and type of the font
you use (font-size and font-type).
The last attribute is dedicated to event binding. This can be used to bind the control to a specific
event. If you implement your own method MyClick, this method will be executed when the
corresponding button is clicked if you use the server control event binding shown in the slide.
Data Binding Expression
You can create bindings between server controls and data sources. The data binding expression is
enclosed by the character sequences <%# and %>. The data-binding model provided by ASP.NET is
hierarchical. That means you can create bindings between server control properties and superior
data sources.
Server-side Object Tags
If you need to create an instance of an object on the server, use server-side object tags. When the
page is compiled, an instance of the specified object is created. To specify the object use the
identifier attribute. You can declare (and instantiate) .NET objects using class as the identifier, and
COM objects using either progid or classid.
Server-side Include Directives
With server-side include directives you can include raw contents of a file anywhere in your ASP.NET
file. Specify the type of the path to filename with the pathtype attribute. Use either File, when
specifying a relative path, or Virtual, when using a full virtual path.
Server-side Comments
To prevent server code from executing, use these character sequences to comment it out. You can
comment out full blocks - not just single lines.
First ASP.NET Program.
Now let us have our First ASP.NET program.
Let’s look at both the markup and the C# portions of a simple web forms application that generates
a movie line-up dynamically through software.
Markup Portion
Web form application part 1 -- SimpleWebForm.aspx
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<% @Page Language="C#" Inherits="MoviePage" Src="SimpleWebForm.cs" %>
<html>
<body background="Texture.bmp">
<TITLE>Supermegacineplexadrome!</TITLE>
<H1 align="center"><FONT color="white" size="7">Welcome to
<br>Supermegacineplexadrome!</FONT></H1>
<P align="left"><FONT color="lime" size="5"><STRONG>
<U>Showtimes for <%WriteDate();%></U>
</STRONG></FONT></P>
<FONT size="5" color="yellow"><%WriteMovies();%></FONT>
</body>
</html>
And this is where the C# part of a web forms application comes in.
Web form application part 2 - SimpleWebForm.cs
using System;
using System.Web.UI;
using System.Web.UI.WebControls;
public class MoviePage:Page
{
protected void WriteDate()
{
Response.Write(DateTime.Now.ToString());
}
protected void WriteMovies()
{
Response.Write("<P>The Glass Ghost
Response.Write("<P>Untamed Harmony
"6:55 pm</P>");
Response.Write("<P>Forever Nowhere
Response.Write("<P>Without Justice
}
}
(R) 1:05 pm, 3:25 pm, 7:00 pm</P>");
(PG-13) 12:50 pm, 3:25 pm, " + <br>
(PG) 3:30 pm, 8:35 pm</P>");
(R) 12:45 pm, 6:45 pm</P>");
Execution Cycle :
Now let's see what’s happening on the server side. You will shortly understand how server controls fit
in.
A request for an .aspx file causes the ASP.NET runtime to parse the file for code that can be
compiled. It then generates a page class that instantiates and populates a tree of server control
instances. This page class represents the ASP.NET page.
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Now an execution sequence is started in which, for example, the ASP.NET page walks its entire list of
controls, asking each one to render itself.
The controls paint themselves to the page. This means they make themselves visible by generating
HTML output to the browser client.
Execution Process
We need to have a look at what’s happening to your code in ASP.NET.
Compilation, when page is requested the first time
The first time a page is requested, the code is compiled. Compiling code in .NET means that a
compiler in a first step emits Microsoft intermediate language (MSIL) and produces metadata—if you
compile your source code to managed code. In a following step MSIL has to be converted to native
code.
Microsoft intermediate language (MSIL)
Microsoft intermediate language is code in an assembly language–like style. It is CPU independent
and therefore can be efficiently converted to native code.
The conversion in turn can be CPU-specific and optimized. The intermediate language provides a
hardware abstraction layer.
MSIL is executed by the common language runtime.
Common language runtime
The common language runtime contains just-in-time (JIT) compilers to convert the MSIL into native
code. This is done on the same computer architecture that the code should run on.
The runtime manages the code when it is compiled into MSIL—the code is therefore called managed
code.
ASP.NET Applications and Configuration
Overview
Like ASP, ASP.NET encapsulates its entities within a web application. A web application is an abstract
term for all the resources available within the confines of an IIS virtual directory. For example, a web
application may consist of one or more ASP.NET pages, assemblies, web services configuration files,
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graphics, and more. In this section we explore two fundamental components of a web application,
namely global application files (Global.asax) and configuration files (Web.config).
Global.asax
Global.asax is a file used to declare application-level events and objects. Global.asax is the ASP.NET
extension of the ASP Global.asa file. Code to handle application events (such as the start and end of
an application) reside in Global.asax. Such event code cannot reside in the ASP.NET page or web
service code itself, since during the start or end of the application, its code has not yet been loaded
(or unloaded). Global.asax is also used to declare data that is available across different application
requests or across different browser sessions. This process is known as application and session state
management.
The Global.asax file must reside in the IIS virtual root. Remember that a virtual root can be thought of
as the container of a web application. Events and state specified in the global file are then applied to
all resources housed within the web application. If, for example, Global.asax defines a state
application variable, all .aspx files within the virtual root will be able to access the variable.
Like an ASP.NET page, the Global.asax file is compiled upon the arrival of the first request for any
resource in the application. The similarity continues when changes are made to the Global.asax file;
ASP.NET automatically notices the changes, recompiles the file, and directs all new requests to the
newest compilation. A Global.asax file is automatically created when you create a new web
application project in the VS.NET IDE.
Application Directives
Application directives are placed at the top of the Global.asax file and provide information used to
compile the global file. Three application directives are defined, namely Application, Assembly, and
Import. Each directive is applied with the following syntax:
<%@ appDirective appAttribute=Value ...%>
Web.config
In ASP, configuration settings for an application (such as session state) are stored in the IIS
metabase. There are two major disadvantages with this scheme. First, settings are not stored in a
human-readable manner but in a proprietary, binary format. Second, the settings are not easily
ported from one host machine to another.(It is difficult to transfer information from an IIS’s
metabase or Windows Registry to another machine, even if it has the same version of Windows.)
Web.config solves both of the aforementioned issues by storing configuration information as XML.
Unlike Registry or metabase entries, XML documents are human-readable and can be modified with
any text editor. Second, XML files are far more portable, involving a simple file transfer to switch
machines.
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Unlike Global.asax, Web.config can reside in any directory, which may or may not be a virtual root.
The Web.config settings are then applied to all resources accessed within that directory, as well as its
subdirectories. One consequence is that an IIS instance may have many web.config files. Attributes
are applied in a hierarchical fashion. In other words, the web.config file at the lowest level directory is
used.
Since Web.config is based on XML, it is extensible and flexible for a wide variety of applications. It is
important, however, to note that the Web.config file is optional. A default Web.config file, used by all
ASP.NET application resources, can be found on the local machine at:
%winroot%Microsoft.NetFrameworkversionCONFIGmachine.config
Summary
ASP.NET is an evolution of Microsoft’s Active Server Page (ASP) technology. Using ASP.NET, you can
rapidly develop highly advanced web applications based on the .NET framework. Visual Studio Web
Form Designer, which allows the design of web applications in an intuitive, graphical method similar
to Visual Basic 6. ASP.NET ships with web controls wrapping each of the standard HTML controls, in
addition to several controls specific to .NET. One such example is validation controls, which intuitively
validate user input without the need for extensive client-side script.
In many respects, ASP.NET provides major improvements over ASP, and can definitely be considered
a viable alternative for rapidly developing web-based applications.
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